This invention relates to a method of producing a transparent electromagnetic wave shielding plate for shielding electromagnetic waves and the transparent electromagnetic wave shielding plate produced thereby, more particularly a method of forming an electrode section which can be easily grounded to exhibit the electromagnetic wave shielding effect for a transparent electromagnetic wave shielding plate used as the front plate to be disposed on the front face of a display panel for plasma display (hereinafter sometimes referred to as plasma display panel (PDP)) and medical equipment, and a transparent electromagnetic wave shielding plate having the electrode section and electromagnetic wave shielding front plate for a PDP.
Recently, a number of electronic devices utilizing, e.g., electrical, electronic and wave devices, have spread as a result of progress of electronic technologies. Some of these devices radiate electromagnetic waves harmful to human and other devices, which has been increasingly causing problems. Therefore, the countermeasures against these problems are becoming very important.
It is reported that large quantities of harmful electromagnetic waves of non-ionized ray, e.g., microwaves and radio waves, are emitted from surfaces of displays, e.g., those for a variety of computers (e.g., office and factory automation devices), game machines and TV sets. Recently, adverse effects of these electromagnetic waves on human health have been pointed out, and their interference with other devices gives rise to social problems.
More recently, a plasma display panel (PDP) as light-emitting, planar display panel has been attracting attention as a large-size display excellent in visibility. However, the PDP emits more intense electromagnetic waves leaking out of the front face than the conventional display panel, e.g., cold-cathode ray tube (CRT) or liquid crystal display panel (LCD), and hence is strongly required to have a better electromagnetic wave shielding function.
The troubles caused by electromagnetic waves are generally controlled by electromagnetic wave shielding materials. An electromagnetic wave shielding material covers an electronic device, building or the like to prevent penetration of the waves from the outside, or to contain the waves inside. Some of the applicable areas for electromagnetic wave shielding materials are front plates for PDPs, and transparent plates disposed on, e.g., front faces of a variety of electronic and medical devices, to shield electromagnetic waves for these devices.
The transparent electromagnetic wave shielding plate, which can find various applicable areas, must be grounded to exhibit its inherent electromagnetic wave shielding effects. In other words, it can fully exhibit its electromagnetic wave shielding effects, when it is ground from its outer surface, preferably from its entire outer surfaces.
It is very advantageous for the transparent electromagnetic wave shielding plate, which is in the form of plate, to have the electrode section exposed to the inner surface inside of the assembly, because it can be mounted on a variety of devices and connected to the outside terminals for grounding from its outer surface by simply pressing the plate to the outer frame of the device.
A transparent electromagnetic wave shielding plate formed using a hot-bonding film is disclosed by, e.g., Japanese Patent Laid-Open No. 292575/1999 as an electromagnetic wave shielding type light-permeating window panel material
The publication proposes a method of forming an electrode section comprising electroconductive members extended to the outside of the outer surface of a formed article on which it is to be mounted, in such a way that it is rolled into the inside of the inner surface and fixed by means of an electroconductive adhesive tape to finally form the electrode section on the inner surface of the formed article""s front face. This method, however, is disadvantageous in that it requires much labor and skillfulness for forming the electrode section.
It involves another disadvantage that the electroconductive member is limited to a form of flexible fibrous meshes, because the electrode is rolled into the inside of the inner surface, and a film-shaped electroconductive member, e.g., metallic mesh film, cannot be used for its rigidity.
Techniques for heat-bonding a variety of members to each other into a monolithic laminate by hot pressing using a heat-bond film are disclosed by Japanese Patent Laid-Open Nos. 352318/1999 and 28813/2000, where the hot-bonding film used for these inventions can simultaneously bond a number of members into a monolithic laminate, fast under heating to be molten or under pressure.
These known or traditional methods can propose production of a monolithic laminate of heat-bond film, transparent optical film and electroconductive member which is wider than these films and positioned inside of them, to have the electrode section on the inner surface of the formed article. These methods, however, have a disadvantage that the electroconductive member may not be securely exposed to the inner surfaces, when the heat-bond film is molten and oozes out during the hot-bonding step to cover the electroconductive member surfaces.
Reducing size of the heat-bond film further to avoid oozing-out of the film may form defects in the space between the film and outer transparent optical film. Therefore, it is practically impossible to control melting and oozing-out of the heat-bond film.
It is an object of the present invention to provide a method of forming an electrode section on the inner surface of a transparent, electromagnetic wave shielding plate, which can solve the problems involved in the conventional transparent, electromagnetic wave shielding plate, allow its transparent substrate, electroconductive member and transparent film to be fast adhered to each other, and also allow the plate to be easily grounded. It is another object of the present invention to provide the transparent, electromagnetic wave shielding plate and electromagnetic wave shielding front plate for PDP""s produced by the same method.
The inventors of the present invention have found that a frame member almost as thick as the heat-bond film, provided to replace the perimeter or part of the heat-bond film corresponding to the electrode section, can stop movement of the heat-bond film which is molten under heating and pressure for laminating the plate components by hot pressing, and that removing part of the transparent optical film as the outer layer and frame member, both corresponding to the electrode section, can easily expose, to the surface layer section, the portion of the electroconductive section of the electroconductive member which is immediately below the heat-bond film, to form the electrode section on the inner surface, reaching the present invention.
The first invention provides a method of forming an electrode section on the inner surface of the transparent, electromagnetic wave shielding plate, composed of a transparent substrate coated, at least on one side, with an electroconductive member and transparent film in this order, which are laminated into a monolithic structure via a heat-bond film, comprising:
(a) laminating the components of the transparent, electromagnetic wave shielding plate by hot pressing into the monolithic structure, after replacing the perimeter or part of the heat-bond film corresponding to the electrode section by a frame member almost as thick as the heat-bond film,
(b) removing the frame member and part of the outer transparent film, both corresponding to the electrode section, or only the outer transparent film for the part corresponding to the electrode section, and
(c) exposing the electroconductive section of the electroconductive member to the surface layer section by the above steps (a) and (b).
The second invention provides the method of the first invention for forming an electrode section on the inner surface of the transparent, electromagnetic wave shielding plate, wherein the transparent film is coated with a tackifier layer on the inner surface.
The third invention provides the method of the first or second invention for forming an electrode section on the inner surface of the transparent, electromagnetic wave shielding plate, wherein the electroconductive member is an electroconductive mesh.
The fourth invention provides the method of the first or second invention for forming an electrode section on the inner surface of the transparent, electromagnetic wave shielding plate, wherein the electroconductive member is an electroconductive film.
The fifth invention provides the method of the first or second invention for forming an electrode section on the inner surface of the transparent, electromagnetic wave shielding plate, wherein the electroconductive member is a transparent substrate surface-treated to be electroconductive.
The sixth invention provides a transparent, electromagnetic wave shielding plate which has the electrode section formed by one of the first to fifth inventions.
The seventh invention provides the transparent, electromagnetic wave shielding plate of the sixth invention, wherein an electroconductive gasket having an almost circular or angular cross-section is set on the electrode section.
The eighth invention provides the transparent, electromagnetic wave shielding plate of the sixth or seventh invention, wherein the frame member is electroconductive.
The ninth invention provides an electromagnetic wave shielding front plate for plasma display panels which uses the transparent, electromagnetic wave shielding plate of one of the sixth to eighth inventions.